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Joong Tark Han

Publications and source records attributed to Joong Tark Han.

7 recordsLinked to original sources
PubMed2006

Photoreversibly switchable superhydrophobic surface with erasable and rewritable pattern.

We report the facile fabrication of a functional nanoporous multilayer film with wettability that is reversibly tunable between superhydrophobicity and superhydrophilicity with UV/visible irradiation. Our approach controls surface roughness with an electrostatic self-assembly process and makes use of the photoresponsive molecular switching of fluorinated azobenzene molecules. Selective UV irradiation onto the nanostructured substrate was used to realize substrates with erasable and rewritable patterns of extreme wetting properties. Our findings will open up new avenues for external stimuli-responsive smart surfaces.

Journal Article↗
PubMed2006

Two modes of transformation of amorphous calcium carbonate films in air.

Large-area amorphous calcium carbonate (ACC) films in air are shown to be transformed into crystalline calcium carbonate (CaCO(3)) films via two modes-dissolution-recrystallization and solid-solid phase transition-depending on the relative humidity of the air and the temperature. Moisture in the air promotes the transformation of ACC into crystalline forms via a dissolution-recrystallization process. Increasing the humidity increases the rate of ACC crystallization and gives rise to films with numerous large pores. As the temperature is increased, the effect of moisture in the air is reduced and solid-solid transition by thermal activation becomes the dominant transformation mechanism. At 100 and 120 degrees C, ACC films are transformed into predominantly (110) oriented crystalline films. Collectively, the results show that calcium carbonate films with different morphologies, crystal phases, and structures can be obtained by controlling the humidity and temperature. This ability to control the transformation of ACC should assist in clarifying the role of ACC in the biomineralization of CaCO(3) and should open new avenues for preparing CaCO(3) films with oriented and fine structure.

Air↗
PubMed2005

Stable superhydrophobic organic-inorganic hybrid films by electrostatic self-assembly.

Organic-inorganic hybrid films were prepared through layer-by-layer (LBL) deposition of poly(allylamine hydrochloride) (PAH) and ZrO(2) nanoparticles coated with poly(acrylic acid) (PAA), allowing facile control of surface roughness and hydrophobicity. Superhydrophobic behavior was observed after deposition of silica nanoparticles and a simple fluorination of the surface. The structure of films was controlled by the number of deposition cycles using PAA-coated 100 nm ZrO(2) nanoparticles, the particle size, and the prelayer with PAH and PAA. The change in the apparent water contact angle of (PAH/PAA-coated ZrO(2)n surfaces without fluorination of the surface agrees with Cassie and Baxter's model for nonwetted surfaces even though the outermost surface itself is hydrophilic. Superhydrophobic surfaces were then successfully developed by the deposition of hydrophilic silica nanoparticles on a 10 bilayer surface of PAH/PAA-coated ZrO(2), and a simple fluorination. Moreover, the chemical stability of the film was greatly increased by heat-induced cross-linking of the film. The incorporation of ZrO(2) nanoparticles in superhydrophobic films promises better mechanical properties than the organic film.

Acrylic Resins↗
PubMed2005

Diverse access to artificial superhydrophobic surfaces using block copolymers.

The creation of an artificial superhydrophobic surface with micro- and nanostructures has been demonstrated using a block copolymer micelle solution and silica nanoparticles. The unique technique of a nanoparticle-supported micelle stabilization together with changes in the solvent power guarantees the precise morphology control of certain block copolymer-mediated surfaces. The approaches presented here provide a new strategy for the fabrication of a wettability-controlled organic-inorganic hybrid or organic coatings.

Journal Article↗
PubMed2005

Deposition of amorphous calcium carbonate hemispheres on substrates.

The amorphous calcium carbonate (ACC) hemispheres were deposited on the mica and poly(diallyldimethylammonium chloride) modified surface. The form of the ACC deposit on the substrates can be controlled by modifying the substrate surface, the introduction of additives, or both. It demonstrated that substrates (insoluble matrix) and additives (soluble macromolecules) have significant influence on the crystallization of CaCO(3).

Journal Article↗
PubMed2004

Fabrication of superhydrophobic surface from a supramolecular organosilane with quadruple hydrogen bonding.

A supramolecular organosilane, 2-(3-(triethoxysilyl)propylaminocarbonylamino)-6-methyl-4[1H]pyrimidinone comprising quadruple hydrogen bonds has been synthesized in one step from commercially available starting materials. The synthesized supramolecular organosilane can be stabilized and phase-separated by dimerization via the linear array of quadruple hydrogen bonds in solution. This property of the supramolecular organosilane has been exploited to fabricate structuring materials having a superhydrophobic surface property. We have successfully generated the interconnected granular structure with adequate roughness for superhydrophobicity via sol-gel process.

Journal Article↗